1. Field of the Invention
This invention relates to a semiconductor apparatus including a semiconductor element, and particular to a cooling structure for the semiconductor element such as a power MOSFET or an IGBT.
2. Description of the Related Art
A semiconductor element (semiconductor chip) such as power MOSFET or an IGBT controls large current, and accordingly produces a large amount of heat. Therefore, as a manner for cooling the semiconductor chip, various constitutions utilizing an air-cooling type radiation fin, a water-cooling type cooling block, and the like for removing heat from the semiconductor chip have been proposed by JP-A-62-92349, JP-A-63-96946, JP-A-62-141751, JP-A-61-265849, JP-A-3-20065, and the like.
However, the conventional constitutions have the following problems in a practical usage. For instance, a large size of the radiation fin is required to increase a radiation amount. When a water-cooling type cooling member is used to improve a radiation efficiency, water as refrigerant necessitates a passage thereof. The passage constitution is liable to be complicated to complicate the apparatus and to increase the size of the apparatus as a whole.
When a radiation member is attached to the semiconductor element, assembling time may be lengthened according to an arrangement of the two members. Further, because the radiation member assembled with the semiconductor element makes the semiconductor apparatus complicated and sized larger, the mountability of the semiconductor apparatus deteriorates especially when the semiconductor apparatus must be mounted in a limited space within an automotive engine room when it is used for an inverter of an electric vehicle.
When the semiconductor apparatus includes several semiconductor elements, there arise problems such that radiation members must be assembled with the respective semiconductor elements, the arrangement of the semiconductor elements may be limited according to the arrangement relationship with the radiation members, and the like. Each radiation member and each semiconductor element generally contact with each other through an insulation substrate for holding the semiconductor element, and a radiation passage for transmitting heat from the semiconductor element to the radiation member is provided to improved the radiation property. In this case, radiation grease is disposed between the both members to fill gaps produced by surface irregularity and waviness to enhance adhesiveness therebetween. However, because the radiation grease includes oil as a main component, the viscosity of the grease is lowered by heat produced from the element (for instance, at 150° C. or more). The grease with the lowered viscosity is liable to flow out to deteriorate the adhesiveness described above, resulting in deterioration of the radiation property.